As exposed by Sagan, the traditional solipsism that humans are used to exhibit when describing themselves and their position in the universe, is not sustainable . Humans have gradually stopped believing they were the center of the universe and the summit of all creation, and started being displaced until becoming just inhabitants of an insignificant part of the periphery of the galactic neighborhood.
Apparition of life on earth appears to be miraculous, but in fact is more common and resilient than most like to think it is. Most of the species that have existed on earth have become extinct , yet life seems to thrive when conditions for its origins and maintenance are met .
The mediocrity principle assumes that there are billions of stars in this galaxy, a great number of them are second generation medium-sized stars, just like the sun, that could harbor planets with liquid water on them, many of them would be able to sustain life, and the earth is just one of such planets . This would indicate that statistically the galaxy must be full of life, and if it is given enough time, say 5 to 10 billion years of uninterrupted evolution, intelligence and civilizations would appear in many places, though at different times .
But, if life and intelligence are so common, humans should have found signals of it in every corner of the galaxy by now, given the effort they put on developing programs like the SETI, and that is part of the unsolved Fermi Paradox . The most optimistic solipsist point of view asserts that the possible number of intelligent species in a galaxy like the Milky Way is probably just one, which means that humans are surely alone in the galaxy . This is not to say that there are not any other forms of life in the galaxy, it would just mean that the evolutionary process to develop high intelligence is way more complicated than the appearance of living molecules. Intelligence is a relatively new phenomenon in Earth´s evolutionary history, and it has only occurred in just one of all the billions of species that have existed so far. This could be a sign that intelligence might not be a desirable quality for all species, or that it requires higher amounts of energy, making it a really inefficient trait .
Assuming that one intelligent form of life thrives and reaches a point where interstellar travel is possible, there is a chance that they would create self-replicating machines that would colonize the galaxy in a couple hundred millions of years . If that is the case, humans should have encountered signs of the existence of such machines, or would be on the verge of creating their own . Since humans have not encountered such machines, or signs of their existence, that would probably mean that they are alone in the galaxy .
However, these arguments do not in any way prove that intelligence does not exist, it merely means that either humans are still too primitive to be able to effectively explore the galaxy, or intelligent life on other planets have not yet reached the technical advances needed for interstellar communication.
It is now known that the molecules necessary to start the cycles of life are fairly common in the universe, and there are billions of worlds that could sustain and maintain such cycles, and that is accepted even by some of the deniers of extraterrestrial life (See Mayr). Given that there is a great chance that some of those planets are older than the Earth, there must be some that contain intelligent life . The fact that humans have not been able to contact any of those other worlds, might be due to the relative novelty of telecommunications; of the three hundred thousand years of the apparition of intelligence, humans have been able to use telecommunications for a mere hundred years . In relation with the invention of self-replicating machines to colonize worlds, such an invention does not seem to be what rational beings would take as a first choice for colonization, given that they would eventually consume the whole galaxy just to fulfill their reproductive purpose .
Chances are that most of the civilizations present in the galaxy, have not yet reached a point where interstellar communication is a possibility. Only one year ago the human race made contact with the first interstellar object, the Voyager 1, and it is merely a primitive probe made by humans themselves launched more than thirty years ago . One should expect that other civilizations that have reached certain technical level should be looking for signs of intelligence at the same time as well, but most of the planets that could possibly harbor such intelligence are hundreds of light years away.
Humans believed Europe, Africa and Asia were the only places in which to find intelligence because they had not seen any signal of the contrary until 1492, and they happened to be completely wrong. Believing that they are the only intelligent beings in the galaxy just because they have not found signs of other civilizations in the tiny corner they happen to inhabit, is just a sign that the solipsist vision of the universe has not yet been abandoned, and they might prove to be wrong anytime now.
Works Cited
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